Preparation Of Composite Particles By Rapid Expansion Of Supercritical Solution

The preparation technology of composite particles can not only solve the problem of fine particles agglomeration, but also change the functional characteristics and surface reaction characteristics of the fine particles. Good characteristics can be obtained by surface coating, which is very important for the practical design and extensive application of composite particles. It has a broad prospect for the composite particles used in the fields of chemical engineering, structure material, military and biological industry.The rapid expansion of supercritical solution (RESS) technology is a new method for the preparation of composite particles. It has incomparable advantages over the traditional methods in the treatment of heat sensitive and bioactive materials because of its mild operation conditions. At present, it is still in preliminary experiment stage using RESS technology to prepare composite particles and many problems have to be faced with.An improved RESS technology is presented in this paper. The coating of fine particles using wax, benzoic acid and lactic acids were studied respectively by experiment. The influences of extraction pressure, extraction temperature, pre-temperature and impinging distance on coating effect were investigated.The optional microscope, SEM and TGA were adopted to characterize the composite particles. The results show that the coating of fine particles can be accomplished by the improved RESS process and the thickness of the coating layer of composite particles can be controlled. The coating layer prepared by this process is continuous, uniform and combining without obvious agglomeration.Over the investigated range of the experiments, the thickness of coating layer increases with the increase of pressure, pre-temperature and impinging distance. The extraction temperature has little effect on the coating layer. Therefore, the extraction pressure, pre-temperature and impinging distance are the main influencing factors.The research in this paper provides the preparation of composite particles with a new method. Moreover, the influences of process parameters on the thickness of coating layer were obtained and the experimental results can be used as necessary fundamental datum for further study.